Welded Structures Research Articles

A strength estimation method for aluminum alloy butt welded joints with mismatched mechanical properties

Aluminum alloy thin-walled welded structures have been widely used in automotive lightweight design. However, during the welding process of aluminum alloy sheets, the mismatched welded joints with different microstructure and mechanical properties are formed. The entire mismatched welded joint can be divided into four zones, including welded zone (WZ), hardening heat affected zone (HZ), softening heat affected zone (SZ) and base metal zone (BM). This study aims to analyze the effects of mechanical properties and geometrical characteristics of different welding zones on the load-bearing capacity of aluminum alloy thin-wall welded structures. According to experimental results, the relationship between hardness and ultimate tensile strength was investigated. And then, a tetra-material model of mismatched welded joints was established based on the hardness distribution, and the strength of mismatched welded joints was systematically investigated by numerical simulation. Additionally, the statistical analysis of the relationship between mismatched parameters and the strength of welded joints was conducted through the design of experiments (DOE). The results show that the existence of SZ exerts a crucial role in the loading capacity of the welded joint. The main effects and interactions of geometrical and mechanical properties parameters have a great influence on the load-bearing capacity of welded joints. Moreover, the proposed meta-models could effectively predict the strength of thin-wall welded structures, providing a guideline for evaluating the load-bearing capacity of the complex components with the welded structures.

Damage Occurrence in Welded Structures of the Bucket-Wheel Boom

Causes of damage occurrence in vital components of welded structures of the bucket-wheel excavator boom (DU1) at the coal landfill of the thermal power plant 'Nikola Tesla A' in Obrenovac (Serbia) are investigated. Bucket-wheel excavator was produced by French company 'Ameco' and it moves along the circular track. Taking into account lack of technical documentation, all tests and were carried out under the assumption that welded structures were made of structural steels S355 and S235. Investigation of causes of damage occurrence are based on results of non-destructive tests (NDT) and tensometric measurements.

Evaluation of local stress‐based fatigue strength assessment methods for cover plates and T‐joints subjected to axial and bending loading

AbstractThis study aims to find suitable fatigue assessment methods for welded structures (cover plates and T‐joints) subjected to axial and bending loading. The Hot Spot Stress (HSS), 1‐mm stress (OM), Theory of Critical Distances (TCD), Stress Averaging (SA), and Effective Notch Stress (ENS) methods are evaluated in terms of accuracy and reliability. The evaluation is based on fatigue test data extracted from the literature and carried out in this study. It is found that the SA method can be used to assess the fatigue strength of cover plate joints under axial loading with relatively good accuracy and low scatter, followed by the ENS method. The HSS, TCD, SA, and ENS methods are conservative estimation methods for T‐joints under bending, while the accuracy is low. Furthermore, fatigue design curves applicable for T‐joints under bending are discussed, which can be used in the TCD method and SA method.

Comparative analysis of methods for reducing residual stresses in welded structures made of austenitic steels

In this article, the authors conducted a comparative analysis of methods for removing residual stresses in welded structures. The reasons for the formation of residual stresses and methods of their removal are given.

Spot Weld Inspections Using Active Thermography

Spot welds have a significant part in the creation of automotive vehicles. Since the integrity of, for example, a car, is dependent on the performance of multiple welds, it is important to ensure the quality of each spot weld. Several attempts have been made in order to determine the quality of spot welds, but most of them do not focus on the applicability in the manufacturing process. Spot weld inspections are often performed using back heating. However, during manufacturing, robotic inspections are desired, and since the bodywork of a car is a complex shape, the accessibility from the inside of the vehicle is minor. Therefore, inspections using front heating are more suitable. In this manuscript, multiple excitation methods are compared as well as different post-processing techniques. The used excitation techniques can be divided into light heating and inductive heating. Light heating is further divided in lock-in thermography and pulse thermography. The used post-processing techniques are principle component analysis and fast Fourier transform. Inductive heating turns out to be the most suitable measurement technique since it is fast and can be performed as front and back heating. Both investigated post-processing techniques deliver suitable information, such as relief images and information of the internal structure of the spot weld.

On the Accurate Prediction of Residual Stress in a Three-Pass Slot Nickel-Base Repair Weld by Numerical Simulations

The activities within a European network to develop accurate experimental and numerical methods to assess residual stresses in structural weldments are reported. The NeT Task Group 6 or NeT-TG6 project examined an Alloy 600 plate containing a three-pass slot weld made with Alloy 82 consumables. A number of identical specimens were fabricated and detailed records of the manufacturing history were kept. Parallel measurement and simulation round robins were performed. Residual stresses were measured using neutron diffraction via five different instruments. The acquired database is large enough to generate reliable mean profiles, to identify clear outliers, and to establish the systematic uncertainty associated with this non-destructive technique. NeT-TG6 gives a valuable insight into the real-world variability of diffraction-based residual stress measurements, and forms a reliable foundation against which to benchmark other measurement methods. The mean measured profiles were used to validate the accuracy achieved by the network in the prediction of residual stresses.

Fatigue life prediction of gasoline storage tank considering varying current density and weld stress

In the field of corrosion fatigue crack research, how to couple corrosion and fatigue under various conditions is a problem worthy of discussion. According to the electrochemical corrosion principles and the superposition principles, studies have been made on the interaction between corrosion and fatigue, and the relationship model between the corrosion fatigue crack size and the corrosion fatigue remaining life in the Corrosion of Hydrogen evolution (COHE) fatigue long crack growth stage is established. The feasibility of the model is verified by using the experimental data. According to the specific structure of the dislocation butt weld of large storage tank, the stress at the crack is calculated. Based on the above model and the experimental data, the corrosion fatigue residual life of large storage tank is predicted. The feasibility of the model is verified, which provides a new method for corrosion fatigue life prediction of large storage tanks.

Fine Structure and Fracture Surface of Low-Carbon Steel Welds

Fine Structure and Fracture Surface of Low-Carbon Steel Welds

Micro-crystallographically unraveling strength-enhanced behaviors of the heavy-thick Ti-6Al-4V welded joint

Developing high-strength welded joint of heavy-thick titanium alloy plates is in immediate need to unravel the strength-enhanced behaviors for high-pressure and low-temperature performance of deep-sea submersibles. Here, we synergistically employed transmission electron microscope (TEM) and electron back-scattered diffraction (EBSD) technologies to micro-crystallographically unravel the evolution behaviors of weld microstructure, grain orientation and grain boundaries for the welded joint of the heavy-thick Ti-6Al-4V plates with the thickness of up to 60 mm. Resulted, the strength-enhanced welded joint was evidently ascribed to the transformation of lath martensite into basketweave-martensite and the rigid-flexible mixture strategy of the enhanced conical-texture and the weakened basal-texture and cylindrical-texture. Furthermore, the remarkably lowered geometrically necessary dislocations (GNDs) density and the greatly decreased deformation-prone grains number due to the transformation of low-into-high angle grain boundaries indispensably strengthened the joint strength. Therefore, this work has made clear the strength-enhanced behaviors of Ti-6Al-4V welded joints for substantially improving high-strength welded structure of heavy-thick titanium alloy plates, and sufficiently promoting the service safety for deep-sea submersibles. • Transformation of lath martensite into basketweave-martensite enhanced the welded joint strength. • Thermal cycling caused the rigid-flexible mixture of the enhanced conical-texture and the weakened basal-texture. • Transformation of low-into-high angle grain boundaries lowered GNDs density and decreased deformation-prone grains number.

Influence of pulsed-arc welding modes on the structure and mechanical properties of welds and haz metal of welded joints of 30Kh2N2MDF steel

The Paton Welding Journal, 2022, №05. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.

Structure and Mechanical Properties of High Strength Steel 960QL Weldments

The need for welded structures of high-strength steels requires detailed studies on the factors influencing the behaviour of these steels during welding. The present work introduces results on the influence of the welding gap on the structure and some mechanical and technological properties of welded joints of high-strength steel S960QL, joined by submerged arc welding.

Numerical Investigation of the Influence of Ultimate-Strength Heterogeneity on Crack Propagation and Fracture Toughness in Welded Joints.

The mechanical properties of dissimilar metal-welded joint materials are heterogeneous, which is an obstacle to the safety evaluation of key welded structures. The variation of stress–strain conditions at the crack tip caused by mismatch of material mechanical properties in dissimilar metal-welded joints is an important factor affecting crack propagation behavior. To understand the influence of uneven distribution of ultimate strength of the base metal and the welded metal on the crack propagation path, fracture toughness, as well as the mechanical field at the crack tip in the small-scale yield range, the user-defined field variable subroutine method is used to express continuous variation characteristics of welded joint ultimate strength in finite element software. In addition, the J-integral during crack propagation is calculated, and the effect of the ultimate strength on the J-integral and the stress field at the crack tip are analyzed. The results show that as the crack propagation direction is perpendicular to the direction of ultimate strength, the gradient of ultimate strength increases from |Gy|= 50 to |Gy|= 100 MPa/mm, the crack deflection angle increases by 0.018%, and the crack length increases by 1.46%. The fracture toughness of the material decreased slightly during crack propagation. Under the condition that the crack propagation direction is the same as the direction of ultimate strength, the crack propagation path is a straight line. As the gradient of ultimate strength increases from Gx = 50 to Gx = 100 MPa/mm, the crack propagation length decreases by 5.17%, and the slope of fracture toughness curve increases by 51.63%. On the contrary, as the crack propagates to the low ultimate strength side, the crack propagation resistance decreases, the ultimate strength gradient increases from Gx = −100 to Gx = −50 MPa/mm, and the slope of the fracture toughness curve decreases by 51.01%. It is suggested to consider the relationship between crack growth behavior and ultimate strength when designing and evaluating the structural integrity of cracks at the material interface of dissimilar metal-welded joints.

Fatigue Life Prediction of Butt Weld Joint with Weld Defects at Multiple Locations

A numerical model developed using finite element software is used to determine the fatigue life of an arc-welded butt joint with weld defects: lack of penetration, lack of fusion, and undercut, which occur predominantly in welded structures. High-strength, tempered, and quenched fine grain ASTM A517 grade F structural steel, widely used in welded structures, is selected as the base material. The finite element analysis approach adopted in the present work is validated using the experimental and analytical results by performing a benchmark study. The validated numerical approach is then used to generate datasets for developing an empirical model for predicting the fatigue life of a butt joint with defects, modelled as cracks at specific locations, subjected to bending and/or membrane stresses. An experimental investigation was undertaken to validate the empirical model. The influencing parameters are ranked based on their severity on the fatigue life of butt joint.

Electrical and thermal stability of Al-Cu welds: Performance benchmarking of the hybrid metal extrusion and bonding process

Advances in joining processes for aluminum and copper are sought after to facilitate the greater adoption of aluminum in electrical applications. Aluminum's chemical affinity to copper causes the joining and lifetime of Al-Cu welds to be vulnerable to the formation of various intermetallic compounds. Intermetallic compounds and the resulting weld structure are known to reduce the structural integrity and increase the electrical resistance of Al-Cu welds. In this study we evaluate the novel joining process, Hybrid Metal Extrusion and Bonding, for butt welding aluminum and copper. The weld structure was examined using scanning and transmission electron microscopy, and the weld resistance was measured using four-point measurements forecast to the weld interface. Energy dispersive spectroscopy and electron diffraction zone axis patterns were analysed to identify intermetallic compounds. Weld samples were examined pre and post heat treatment at 200 °C, 250 °C and 350 °C for total durations of over 1000 h. The results are compared to existing Al-Cu joining processes, and a new metric, weld interface resistivity, is proposed to compare the electrical properties of bimetallic welds. The Hybrid Metal Extrusion and Bonding process was found to form a thin, consistent and straight intermetallic layer with negligible impact on electrical resistance in the as-welded condition. Artificial ageing of samples by heat treatment established the overall growth rate of intermetallic compounds. The growth rate was used to evaluate the weld's operational lifetime versus temperature. The intermetallic growth rate of Hybrid Metal Extrusion and Bonding was quantified at 200 °C and compared to alternative processes. The Hybrid Metal Extrusion and Bonding process showed a significant performance advantage requiring the longest time to reach 2 μm thickness. Furthermore, the growth of intermetallic compounds did not increase the electrical resistance of the weld interface. The negligible impact on electrical resistance and slow intermetallic growth are promising results of the potential functional performance. This study is the first characterisation of the Hybrid Metal Extrusion and Bonding process for electrical applications showcasing its exciting potential for the joining of aluminum and copper.

Optimization design of excitation coil for pulsed eddy current testing of laser welding defect structure of power battery bus-bar

Pulsed eddy current testing is suitable for non-contact detection of conductor structural defect, which is an effective method to realize online detection of welding structural defect of power battery pack. Aiming at the circular laser weld structure between the bus-bar and the terminal of the power battery pack, a three-dimensional finite element simulation model of pulsed eddy current testing is established. According to the structural parameters of the pulsed eddy current excitation coil, which are the inner diameter, outer diameter, height and number of turns, the pulsed eddy current voltage responses of the laser welding defect structure of the battery pack bus-bar are calculated, respectively. By analyzing the influence of the excitation coil parameters on the pulsed eddy current detection results, the pulsed eddy current excitation coil parameters are determined for the testing of laser welding structural defects. It provides a method and basis for the optimal design of the pulsed eddy current detection system for the laser weld structural defect of the battery pack bus-bar.

Effects of material properties and mismatch on unified constraint parameter

In order to develop unified constraint-based fracture assessment method, it needs to investigate the effects of material properties and mismatches on the unified constraint parameter and develop the parameter solutions for cracked structures. In this work, the effects of material properties (yield strength and hardening exponent) and strength mismatch on the in-plane and out-of-plane unified constraint parameter Ad* of semi-elliptical surface cracks in homogeneous and welded plates have been investigated. The results show that the parameter Ad* does not essentially change with yield strength and hardening exponent of materials for cracks in homogeneous plates under bending and tension loads. The parameter Ad* of weld centerline cracks in welded plates under bending and tension loads is essentially independent on the strength mismatch. These advantages of Ad* are conducive to the development of its solutions for homogeneous and welded structures containing cracks. The effect of weld width on Ad* is related to loading mode, mismatch (undermatch or overmatch) and crack size. The mechanism of the influence of material properties, strength mismatch and weld width on Ad* has been explained by its definition and the crack-tip plastic strain distribution. The development and application of Ad* solutions for homogeneous and welded structures also have been discussed.

Fatigue strength evaluation of 5059 aluminum alloy welded joints Considering welding deformation and residual stress

With the transformation and upgrading of shipbuilding industry, aluminum alloy shipbuilding will gradually develop towards energy saving, light weight and environmental protection. As a new generation of trustworthy aluminum alloy structure, 5059 aluminum alloy material has better mechanical properties and corrosion resistance. However, two prominent shortcomings of aluminum alloy welding structure are large welding deformation and low fatigue strength. In order to accurately consider the influence of welding defects, the temperature field simulation program of thin plate welding structure is designed to predict the welding deformation and residual stress. The simulation results of temperature field and welding deformation of typical welded joints are in good agreement with the test results. Moreover, taking welding deformation and residual stress as initial conditions, the fatigue strength class curves of 5059 aluminum alloy welded joints are renewed based on the hot spot stress.

Research on Underwater Wet Laser Self-Fusion Welding Process and Analysis of Microstructure and Properties of TC4 Titanium Alloy Weld.

In order to explore the feasibility of underwater wet laser welding of the TC4 titanium alloy, research on the underwater laser self-fusion welding process was carried out. The weld structure and mechanical properties in both the air environment and the underwater environment were compared and analyzed. The results show that increasing the laser power and reducing the welding speed are beneficial to obtain a larger water depth threshold. Off-focus amount has little effect on water depth threshold; when the laser power is 3000 W and the welding speed is 5 mm/s, and the water depth exceeds 7 mm, a continuous weld cannot be formed. Compared with welding in the air, underwater welding has narrower weld width, smaller heat affected zone and finer crystal grains. The weld structure is mainly composed of α′ martensite and secondary acicular α′ phase, it is distributed in a net basket shape and the grain size at the top of the weld is finer. The hardness of the weld center is above 600 HV0.1, and the residual stress of the underwater welding weld is approximately symmetrically distributed. There is a large tensile stress along the welding direction at the weld, reaching 458 MPa. The larger residual tensile stress leads to the decrease of weld tensile strength, the tensile strength and elongation of the middle sample are only 52% and 77% of the base metal. Furthermore, the fracture mode is typical brittle fracture.

Detection of butt weld of laser-MIG hybrid welding of thin-walled profile for high-speed train

PurposeThis study aims to solve the problem of weld quality inspection, for the aluminum alloy profile welding structure of high-speed train body has complex internal shape and thin plate thickness (2–4 mm), the conventional nondestructive testing method of weld quality is difficult to implement.Design/methodology/approachIn order to solve this problem, the ultrasonic creeping wave detection technology was proposed. The impact of the profile structure on the creeping wave detection was studied by designing profile structural test blocks and artificial simulation defect test blocks. The detection technology was used to test the actual welded test blocks, and compared with the results of X-ray test and destructive test (tensile test) to verify the accuracy of the ultrasonic creeping wave test results.FindingsIt is indicated that that X-ray has better effect on the inspection of porosities and incomplete penetration defects. However, due to special detection method and protection, the detection speed is slow, which cannot meet the requirements of field inspection of the welding structure of aluminum alloy thin-walled profile for high-speed train body. It can be used as an auxiliary detection method for a small number of sampling inspection. The ultrasonic creeping wave can be used to detect the incomplete penetration welds with the equivalent of 0.25 mm or more, the results of creeping wave detection correspond well with the actual incomplete penetration defects.Originality/valueThe results show that creeping wave detection results correspond well with the actual non-penetration defects and can be used for welding quality inspection of aluminum alloy thin-wall profile composite welding joints. It is recommended to use the echo amplitude of the 10 mm × 0.2 mm × 0.5 mm notch as the criterion for weld qualification.

High sensitivity sensor based on mode interference of fiber arc-shaped misaligned welding structure for strain and torsion sensing

We propose a compact and ultrasensitive all-fiber Mach–Zehnder interferometer sensor based on an arc-shaped misaligned structure that can measure strain and torsion sensing. The structure utilizes a single-mode fiber and was fabricated in an optical fiber fusion splicer through simple discharge and fusion splicing steps. The experimental and theoretical investigations of its response revealed an optimal strain sensitivity of up to ~267.17 pm /με¯. In addition, the maximum torsion sensitivities in the clockwise and counterclockwise rotation directions of the fiber cross section were ~ − 1.528 dB/(rad/cm) and ~1.2191 dB/(rad/cm), respectively. Further, the proposed device exhibited low temperature cross sensitivity. Therefore, this single-mode-fiber based core-cladding modal interferometer has great potential in the field of photoelectric sensing due to multiple advantages such as compact size, easy fabrication process, low cost, etc.